Understanding the Numbers

The calculator gives you three key outputs. Furthermore, each tells you something different about your brew:

Brew Ratio

The relationship between coffee and water, written as 1:X. For example, 18g of coffee yielding 36g of espresso is a 1:2 ratio. Moreover, ratio is the single most useful concept for describing the kind of cup you are making.

TDS (Total Dissolved Solids)

TDS measures the strength of brewed coffee as a percentage. As a result, it tells you how concentrated the cup is:

• Filter coffee: 1.15 to 1.45 percent (Specialty Coffee Association recommended range)
• Espresso: 8 to 12 percent
• Cold brew concentrate: 2 to 4 percent

Furthermore, TDS is independent of cup size. A small espresso and a large filter coffee can have very different TDS values even with the same total dissolved solids.

Extraction Yield

Extraction yield is the percentage of soluble compounds you have actually pulled out of the grounds and into the cup. Moreover, the Specialty Coffee Association considers 18 to 22 percent the optimal range:

• Below 18 percent (under-extracted): sour, thin, salty
• 18 to 22 percent (balanced): sweet, complex, clean
• Above 22 percent (over-extracted): bitter, harsh, drying

The Four Variables That Shape Every Cup

The calculator lets you adjust four variables. Furthermore, each one affects extraction in a different way:

Grind Size

Finer grinds expose more surface area, so water extracts more compounds in less time. On the other hand, coarser grinds slow extraction down. As a result, grind is the single most powerful lever for shifting a cup from under-extracted to balanced to over-extracted. Furthermore, when something tastes off, grind is usually the first thing to adjust.

Brew Ratio

The amount of coffee relative to water shapes strength and clarity. Moreover, stronger ratios (more coffee) produce fuller-bodied cups, while lighter ratios (more water) produce cleaner, more aromatic ones. For more, read our pour-over coffee ratio calculator guide.

Contact Time

How long water stays in contact with the grounds. Furthermore, longer contact times extract more soluble compounds. As a result, contact time and grind size work together: a fine grind in a long brew over-extracts, while a coarse grind in a short brew under-extracts.

Water Temperature

Hotter water extracts faster and pulls out more bitter compounds. Cooler water extracts slower and emphasises acidity. Moreover, most filter brewing happens between 90 and 96 degrees Celsius. As a result, light roasts often benefit from higher temperatures (94 to 96), while darker roasts prefer cooler (90 to 92).

For a complete picture of why water matters in coffee, read our guide to water quality in coffee brewing.

The Brewing Control Chart Explained

The Brewing Control Chart is a visual framework developed by the Specialty Coffee Association. Furthermore, it plots TDS (strength) against extraction yield (efficiency) to show where balanced cups sit. As a result, it has become the universal language of coffee extraction.

The chart divides brewing into nine zones:

• Under-extracted and weak: sour and thin
• Under-extracted and ideal strength: sour but full-bodied
• Under-extracted and strong: sour and intense
• Ideal extraction and weak: balanced but watery
• Ideal extraction and ideal strength: the target zone
• Ideal extraction and strong: balanced and intense
• Over-extracted and weak: bitter and thin
• Over-extracted and ideal strength: bitter but full
• Over-extracted and strong: harsh and intense

Moreover, the goal of dialling in any coffee is to land in the middle target zone: 1.15 to 1.45 percent TDS and 18 to 22 percent extraction yield for filter coffee.

How to Use This Calculator

The calculator works best when used to test specific recipe questions. Furthermore, here are three common workflows:

1. Dialling in a New Coffee

Start with the Classic preset for your brewing method. Furthermore, brew the recipe and taste. If the cup tastes sour, adjust grind finer or extend contact time. As a result, you can systematically move towards the balanced zone.

2. Diagnosing a Flavour Problem

If your coffee tastes wrong, plug your current recipe into the calculator. Moreover, the estimated TDS and extraction yield will show whether you are under-extracting, over-extracting, or just brewing weak. As a result, you know exactly which variable to adjust.

3. Exploring Style Differences

Use the Bright and Comfort presets to see how the same coffee can produce very different cups. Furthermore, this is a great way to develop your palate and understand how small changes shape flavour. Read our guide on understanding taste and sensory receptors in coffee to go deeper.

Troubleshooting with the Calculator

When your coffee tastes off, the calculator gives you a precise direction to adjust. Furthermore, the most common scenarios:

• Sour, sharp, or thin. Likely under-extracted. Try a finer grind, hotter water, or a longer brew. Read our guide on why coffee tastes sour.
• Bitter or harsh. Likely over-extracted. Try a coarser grind, cooler water, or a shorter brew. Read our guide on why coffee tastes bitter.
• Weak or watery. Strength issue, not extraction. Try a higher ratio (more coffee per litre of water). Furthermore, the calculator will show TDS rising as you adjust.
• Flat or muted. Often water quality or freshness, not extraction. Read our guide to water quality and our guide to limescale.

More Routes Coffee Calculators

• Pour-Over Coffee Ratio Calculator for simple ratio-based pour-over brewing.
• Interactive Espresso Calculator for dialling in espresso shots.

Brewing Better Coffee with Routes

An extraction calculator is most useful when paired with high-quality, freshly roasted coffee. Furthermore, a Routes Coffee subscription delivers single origins and blends to your door, with detailed tasting notes that complement what the calculator shows. As a result, you can connect what you measure with what you taste, and develop your palate faster.

Frequently Asked Questions

What is TDS in coffee?

TDS stands for Total Dissolved Solids and measures the strength of brewed coffee as a percentage. Filter coffee typically sits between 1.15 and 1.45 percent TDS. Furthermore, espresso ranges from 8 to 12 percent. As a result, TDS tells you how concentrated the cup is, regardless of how much you brewed.

What is extraction yield in coffee?

Extraction yield is the percentage of soluble compounds extracted from the coffee grounds into the cup. The Specialty Coffee Association considers 18 to 22 percent the optimal range. Below 18 percent, coffee tastes sour and under-extracted. Above 22 percent, it tastes bitter and over-extracted.

What is the Brewing Control Chart?

The Brewing Control Chart is a visual framework developed by the Specialty Coffee Association that plots TDS against extraction yield. Furthermore, it identifies a balanced zone where most great cups sit. As a result, it gives brewers an objective way to dial in recipes and diagnose flavour issues.

How does grind size affect extraction?

Finer grinds create more surface area, so water extracts more compounds in less time. On the other hand, coarser grinds extract more slowly. Furthermore, grind is the most powerful lever for shifting between under-extracted (sour) and over-extracted (bitter) cups, even when ratio and time stay the same.

How does water temperature affect coffee flavour?

Hotter water extracts faster and pulls out more bitter compounds. Cooler water extracts slower and emphasises acidity. Furthermore, most filter brewing happens between 90 and 96 degrees Celsius. As a result, light roasts often benefit from higher temperatures (94 to 96), while darker roasts prefer cooler (90 to 92).

Do I need a refractometer to measure TDS?

For precise readings, yes. A coffee refractometer (such as the Atago, VST, or DiFluid) measures TDS to 0.01 percent accuracy. However, this calculator gives you an estimated TDS based on your inputs, which is usually accurate enough for home brewing and dialling in.

What is the ideal extraction yield for filter coffee?

18 to 22 percent extraction yield is the Specialty Coffee Association optimal range. Furthermore, 19 to 21 percent is where most balanced, sweet cups land. As a result, this is the zone to aim for when dialling in any filter recipe.

Can this calculator replace a refractometer?

For home brewing, in most cases yes. The calculator estimates TDS and extraction yield based on your inputs, which is usually accurate enough to dial in recipes and diagnose flavour problems. On the other hand, professional cafes and competition baristas use refractometers for precise, repeatable readings.

Related Reading

• Routes Coffee, How to Brew Better Coffee at Home (pillar)
• Routes Coffee, Mastering Espresso: Key Parameters
• Routes Coffee, Pressure Profiling in Espresso
• Routes Coffee, Why Water Quality Is Important in Coffee Brewing
• Routes Coffee, Why Does Coffee Taste Sour?
• Routes Coffee, Why Does Coffee Taste Bitter?
• Routes Coffee, Understanding Taste and Sensory Receptors

Sources & Further Reading

• Specialty Coffee Association, Brewing Control Chart and Golden Cup standard.
• Barista Hustle, TDS and extraction yield studies.
• Rivera, J. A. Roast Magazine, extraction science.
• VST and Atago, coffee refractometer documentation.